Bladder cancer is a common and deadly disease, but the molecular events leading to its development are incompletely understood. We have recently identified a novel oncogene, Ataxia-Telangiectasia Group D Complementing (ATDC), which drives initiation and progression of bladder tumors in transgenic mice. These tumors are indistinguishable from their human counterparts. ATDC expression is elevated (about 70%) in human invasive bladder cancers and correlates with poorer survival after chemotherapy. In other tumor types, ATDC binds p53, modulates DNA damage responses and up-regulates beta-catenin signaling. In preliminary data, we find that ATDC expression is induced by inflammation, associated with decreased expression of PTEN and RB1, two important tumor suppressor genes implicated in bladder tumorigenesis, and show that ATDC promotes methylation and silencing of the PTEN promoter through upregulation of DNMT3a. We hypothesize that ATDC is a crucial determinant of formation, progression and the cytotoxic response in bladder cancer. To better understand the role of ATDC in bladder cancer, we propose the following studies: AIM 1: To characterize the role of ATDC in bladder cancer initiation, progression and metastasis using novel transgenic mouse models and determine the role of inflammation in inducing ATDC expression in normal urothelium. AIM 2: To characterize the role of PTEN, RB1 and p53 in ATDC-mediated bladder tumor formation and progression using both human and mouse model systems. AIM 3: To determine if ATDC expression in bladder cancer drives progression to invasive disease. AIM 4: To determine if ATDC expression promotes bladder tumor resistance to chemotherapy. These studies will characterize a novel mechanism of bladder tumor development and a valuable transgenic model of bladder cancer. We will also use existing human cell lines and primary human tumor samples to elucidate the molecular mechanisms by which ATDC induces bladder cancer and mediates resistance to chemotherapy. These studies are significant because understanding ATDC's oncogenic activity in bladder cancer may lead to new prognostic biomarkers and improved therapeutic approaches in humans.